1. Field of the Invention
The present invention relates to a continuously variable transmission as well as to a transfer case that includes a continuously variable transmission.
2. Description of the Related Art
FIG. 5 shows a known drive train of an all-wheel-drive motor vehicle. An internal combustion engine 10 is connected through a transmission 12, for example a gearbox, to a transfer case 14 from which an output shaft 16 leads to a drive shaft 18, which is connected to a rear axle differential 20. A further output shaft 22 extends from transfer case 14 and is connected through a further shaft 24 to a front axle differential 26. Such drive trains are known in the most varied configurations.
For various reasons, particularly vehicle movement dynamics reasons, it is advisable to divide the output torque of the transmission 12 to the wheels of the rear axle and the wheels of the front axle according to the driving condition in various ways. That can be accomplished by means of clutches, planetary gear sets, and differentials interconnected in various ways. One possibility consists also in integrating a continuously variable transmission (a transmission having a continuously variable transmission ratio) into the transfer case 14, whose transmission ratio can be changed within a limited range in such a way that according to the operating conditions the wheels of the front axle rotate slightly faster or slightly slower than those of the rear axle.
A continuously variable transmission that can be utilized in such a transfer case is described, for example, in German Patent Publication No. DE 200 11 649 U1. The transmission includes a disk converter and a planetary gear set, which are coupled to each other in such a way that one of three main parts of the planetary gear set is controlled in a continuously variable way by the disk converter, a second part is coupled to the driven shaft of the transmission, and a third part is coupled to an output shaft of the transmission. The disk converter includes a drum as a driving component and a crowned disk as a driven component. The crowned disk has pins that each engage a groove of an associated intermediate disk. Each of the axially adjacent intermediate disks is connected to a radially inner surface of the drum through a one-way clutch. By an eccentric displacement between the drum and the crowned disk, the rotational speed ratio between the drum and the crowned disk can be modified. The known disk converter is relatively complicated in its configuration and has relatively large space requirements.
A continuously variable transmission that has a disk-shaped input element and an output element is known from U.S. Pat. No. 6,327,926. The input element has a radially-inwardly-open annular groove within which coupling elements move, which are each designed with a projecting pin whose enlarged end is received in a corresponding radially-extending groove of the output element. The rotational speed ratio between the input element and the output element changes by an eccentric displacement between the two. The elements have a relatively complex design. Furthermore, the axially-extending pins of the coupling elements must have a high rigidity because they are subjected to bending stresses.
It is an object of the invention to produce a continuously variable transmission that can particularly be used in transfer cases and can be economically manufactured with a compact design.